Separation of coal-oil suspensions



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SEPARATION OF COAL-OIL SUSPENSIONS 3 Sheets-Sheet 1 Filed Jan. 27, 1967kuaaosm xuukuz umm zommuzmtou zuhuvz mutzommzvgh.

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m bbx United States Patent 3,505,201 SEPARATION OF COAL-OIL SUSPENSIONSGordon W. Hodgson, George F. Round, and Jan Kruyer, Edmonton, Alberta,Canada, assignors to Research Council of Alberta, Edmonton, Alberta,Canada Filed Jan. 27, 1967, Ser. No. 612,188 Int. Cl. Cg l/02; C10b49/10 US. Cl. 2088 8 Claims ABSTRACT OF THE DISCLOSURE The presentinvention relates to the separation of slurries into their componentparts and is particularly concerned with the separation of coal-oilslurries by means of flash distillation techniques, wherein the slurryis injected into a reactor, the oil being flash distilled and oil-freecoal char particles being left behind.

The coal-oil slurries may for example be slurries formed as suspensionsof pulverised or finely-divided coal in crude oil in order to facilitatetransportation of coal by pipeline. The pipelined mixture may be movedto points adjacent the market areas of the respective com ponents andprocessed at those points to recover the coal and oil constituents.

The invention is particularly concerned with the thermal separation ofoil and coal from coal-oil slurries whereby the coal component isupgraded. This is to say, the coal char product resulting from thethermal separation process is superior as a fuel to the coal that waspresent in the original slurry.

Pumping a solid, mixed with a suitable fluid carrier through a pipelineas a slurry has been used by industry as an economical means oftransporting certain material. Experimental investigations with a1-inch, 45-ft. long pilot-scale pipeline at the Research Council ofAlberta have indicated the possibility of transporting granular coalwith oil as a carrier. Slurries up to 35% coal by weight could be pumpedat velocities up to 19 ft./sec. without causing pressure gradientsappreciably greater than those encountered when pumping oil alone. Oilwas used in these experiments because it was felt that in actualpractice transportation in crude oil obviates the need to move anessentially unprofitable carrier. Both coal and petroleum are found inabundance in Alberta and large quantities of both fuels are required inthe same general market area of eastern Canada. If the present cost ofpipelining oil, which amount to about 0.2 cent per ton-mile, wereapplied to a slurry of coal-in-oil, transportation charges for coalwould be less than one-third of present railway freight charges.Assuming a 24-inch line With a capacity such as already exists for oilbetween Alberta and the Lakehead, continuous transportation of a 25percent slurry would permit some 20 million tons of coal to be laid downin a year.

One of the most important problems associated with pumping of acoal-inoil slurry is the necessity of economically obtaining a cleanseparation of the two components once the slurry has reached the marketlocality. Two modes of separation have been investigated, separation byclassification in multicyclones and separation by flash va- 3,505,201Patented Apr. 7, 1970 porization in a heated reactor. Flash vaporizationof a mixture of Leduc crude oil and Edmonton coal, using a hot fluidizedsolids reactor has yielded a dry char suitable as a fuel for thermalpower stations and an oil that had undergone little change. The presentinvention is concerned with this thermal separation of a slurry ofcoal-inoil.

The term fluidization is used to describe a certain mechanism ofcontacting granular solids with fluids. Since in this work theapplicants are concerned with a coal-in-oil mixture involving contactingcoal char particles with coal particles and oil fluids, this system maybe used to illustrate the process of fluidization.

The particles being fluidized are granular coal char particles, and thefluidizing gas is recycled process gas. As the gas is passed upwardsthrough the bed, there is a certain flow at which the particles aredisengaged somewhat from each other. In this condition the bed behavesas a fluid, hence the name fluidization. In order to maintain gas flowthrough the bed a finite pressure gradient is required to overcomefriction, and to increase the rate of flow a greater pressure gradientis required. When the pressure drop approaches the weight of the bedover a unit cross-sectional area, the solids begin to move. Thiscondition is known as the onset of fluidization.

When the gas velocity is only slightly above that required for the onsetof fluidization, a state known as a quiescent fluidizing bed results. Inthis state the particles in the bed display little or no mixing,interparticle heat and mass transfer in the bed are then at a minimum.As the fluid velocity is somewhat increased, the bed expands and thesolids tend to mix readily. This state is known as a turbulent fluidizedbed and causes a slight increase in pressure gradient. Further increasein gas mass velocity causes a further increase in pressure gradientacross the bed. If the gas velocity is considerably increased, the bedexpands greatly and a condition of great solids dilution is created. Thesolids are then entrained in the fluid and are carried upwards. Thisstate is known as the dilute fluidized phase. However, with a bedcontaining a wide range of particle sizes dust is carried upwards evenat low gas flow rates.

Gas-solid systems are notorious for possessing nonhomogeneous and labilepore textures. This is largely due to the formation of aggregates ofparticles. When aggregates are present in the bed, the process is calledaggregative fluidization in contrast with particulate fluidization wherethe bed has a homogeneous pore structure. Whereas in particulatefluidization the onset of fluidization is marked by a gentle oscillatingmotion of some of the particles constituting the bed, in aggregativefluidization, the fluid literally begins to bubble through the solid bedin a manner identical to the action observed in bubbling a gas through aliquid. The bubbles of fluid rise through the bed and break up at thesurface of the bed, splashing a few particles of the solid upwards. Asthe fluid velocity is increased, the bubbling action becomes more andmore violent, streamers of solids being ejected to considerabledistances above the bed before returning. These phenomena have beenvisually observed in a preliminary study of a gas coal system in anunheated glass column. In this case it was noticed that the streamerswere very marked and started at about four times the gas mass velocitynecessary to obtain onset of fluidization.

A fluidized system may be used to effect a separation of mixtures ofsubstances some of which are essentially volatile, and the other,non-votatile. The volatile components on being introduced to a hot bedof fluidized particles rapidly absorb the heat of vaporization and jointhe fluidizing gas stream passing through the bed while the non-volatilecomponents remain with the fluidizing particles in fluidization reactor.Thus in the case of slurries of coal in oil, the oil components tend topass out of the reactor while the coal components remain with the coalchar particles in the reactor. One of the main features of the inventionis that at the temperatures required to effect such a separation, thecoal char product resulting from the thermal separation process issuperior as a fuel to the coal that was present in the original slurry,having picked up non-volatile components of the oil. The loss of thesecomponents from the recovered oil is balanced off by the production ofvolatile substances from the coal during the process. These become partof the oil product and process gas stream.

Laboratory experiments have been carried out to illustrate the essentialfeatures of the process.

In the following detailed description of the process reference will bemade to the following drawings:

FIGURE 1 represents a flow diagram;

FIGURE 2 is a detailed diagram of a fluidization reactor, and

FIGURE 3 is a flow diagram showing a possible commercial modification ofthe apparatus of FIGURE 1 following the reactor.

The apparatus shown in FIGURE 1 comprises a feed reservoir 1 designed tocontain coal-oil slurry which is conveyed to slurry-pump 2 which pumpsthe slurry into reactor 3 through conduit 4. The crude oil may beaugmented with an admixture of heavy crude oil and/or asphalts andpetroleum residuums.

Initially the entire apparatus is purged with an inert gas such asnitrogen supplied under pressure from source 5, the'nitrogen flow beingcontrolled by valve 6. Once the apparatus has been purged the gas usedis recycled from the system.

The nitrogen and/ or the recycled gas is delivered to the bottom ofreactor 1 through preheater 7, and enters the reactor via conduit 8 andmaintains the bed of solids in a fluidized state indicated at 9, the bedbeing supported mechanically by a foraminous metal plate 10 seatedimmediately above conical section 11 of the reactor. The reactor isheated by means of electrical heaters indicated at 12.

It will be noted that the upper section 13 of the reactor is of largercross-section than the lower section 14. The larger cross-section at thetop of the reactor causes a reduction in gas pressure and velocity inthat area which facilitates separation of char and dust from ascendingvapors.

Most of the heat necessary for the flash vaporization of the oil and thecarbonization of the coal to a char is supplied by heating wires 12through the temperature of the gas entering the reactor is a factor incontrolling the bed temperature. As shown in FIGURE 2 the reactor may becovered with a layer of asbestos cement 15 in order to reduce heat loss.

It is also contemplated as part of the invention to rely on thecombustion of the products of the reactor, the process gas and the charproduct, as a source of heat for the reaction.

Pressure and temperature in the apparatus is recorded at desired pointsin the line and at several levels in the reactor, by means of manometersand thermometers, not shown.

Hot oil vapors and quantities char particles and dust ascend intocyclone 16 mounted in section 13 of the reactor. The particles settle inthe cyclone and are removed through cyclone leg or conduit 17 whichprotrudes through the reactor wall. Quantities of char are removed fromthe reactor through leg 18, the removal being controlled by solenoidvalve 19.

The slurries studied by applicant comprised a mixture of 70% w./w. Leduccrude oil (38.4 API) and 30% w./w. Edmonton subbituminous coal, whileothers involved mixtures of Lloydminster crude oil and Canmore coal.These were selected to illustrate the process in relation to thepipelining operations for which the process might be used.

The most difiicult fluidized-bed separations are those requiring highheat inputs and those marked by high gas velocities in the fluidizedbed. Thus, a fairly dilute slurry of coal-in-oil such as the above 30-70mixture, and a slurry containing a heavy crude oil such as theLloydminster oil represent very difficult operating conditions, and anyprocess suitable for such conditions can be readily operated for morefavorable conditions of feed. The preferable range of coal concentrationin the slurry is thus 30 to 70 or more weight percent. The preferredrange for the heavy oil component is from zero to an upper value of ormore, a value limited largely by the pipeline flow characteristics ofthe slurry; the greater the heavy oil content, the greater theenrichment of the coal char product. In the laboratory experiments themixture of coal in oil, which for example might be a slurry of aboutl00-mesh coal suspended in crude oil, at a concentration of about 30-40%by weight, is injected into a reactor in which oil is flash vaporisedleaving behind the oilfree coal particles in the form of coal char. Theslurry is introduced into a fluidized bed of coal char particles, thebed temperature being maintained at about 600 F. to about 1000 F. Thevaporized oil is recovered in an overhead stream, and the suspended coalbecomes part of the fluidized bed, which is maintained at apredetermined operating inventory level by appropriate withdrawal of thecoal particles via leg or char-removal conduit 18.

The temperature of the bed in the experimental studies was varied over awide range, the operating limits being determined by the failure of thechar particles to remain dry and free flowing for the lower limit and bya limited heat input for the upper limit. In the laboratory tests thedistillation of oil was incomplete at temperatures below 700 F., withthe etfect that the coal char particles tended to agglomerate andthereby prevent proper fluidization. The preferred reaction temperaturesare in the 900l000 F. range wherein the gross characteristics of therecovered oil are at least as favorable as those of the oil in the feedslurry, and the heating value of the coal char product approaches amaximum. Thus there is evident an unexpected result which may beattributed to the particular configuration of the system, as will becomemore evident below.

Slurry to be delivered to the reactor is maintained under vigorousagitation in feed reservoir 1 located above the top of the reactor,falling directly into the fiuidizing bed. The preferred type of pumpused to transmit the slurry is a Sigma pump (Sigmamotor, Inc.,Middleport, N.Y.). The feed is introduced through the top of the reactorrather than the side with the result that a more complete removal of theoil from the char was rendered possible which in turn, enabled thefluidizer to be operated at a lower temperature than would be possibleotherwise. At a reactor temperature of 900 F., for example, theperceutage of benzene-extractibles was reduced from 1.6 to 0.2% byintroduction of the feed at the top of the reactor.

Within the reactor a bed of solids composed principally of coal charparticles is kept in a constant state of fluidization by means offluidizing hot gas delivered to the bottom of the reactor from thepreheater, and if desired in addition, by means of a stream of inert gassuch as nitrogen.

The quantity of solids in the reactor at any given time was indicated bydetermining the pressure of the bed, and as pointed out above a seriesof manometers is used for this purpose, the manometers indicating thepressure differential between the top of the reactor and taps (notshown) that may be located on the side of the reactor at appropriate ordesired levels. The first tap may for example be placed just above plate10, the second 3 in. above the first and the third 6 in. above thefirst. Draw-oh? of char from the bed, to maintain a constant quantity offiuidizing solids, is accomplished by a pressure-sensitive solenoid plugvalve 19, the pressure-sensitive switch 20 (see FIGURE 2) controllingthe valve responding to pressure changes in bed height. Entrained dustand char thrown up as streamers from the bed are separated by cyclone 16as explained above and collected as part of the total char product.

There is constant formation of gaseous products in the reactor whichresults in a continuous increase in the amount of gas within the systemwhich necessitates constant removal to maintain the desired operatingpressure. During the start-up period the system may be filled with aninert gas such as nitrogen, but after about one hour of operationhowever, less than 5% of the original nitrogen remains in the system aspart of the recirculating gas.

A stream of the vapor formed in the reactor is constantly being divertedinto the cyclone where the treated coal char particles settle out andare removed by gravity at removal point 17. Hot vapors formed from thecoal and the oil pass overhead from the cyclone through conduit 21 andare delivered through line 22 to a watercooled condenser 23. An oil fogand a liquid product result from the initial condensation and areconducted to cyclone 24. The condensed liquid is passed through watertrap 25 and the oil portion collected.

The oil fog from the condenser is preferably delivered from cyclone 24into a moving-wire electrostatic precipitator 26, the moving wire 27acting as a self-cleaning electrode. Where a stationary wire is used itis found that the electrode becomes coated with asphalt and entraineddust. The outside wall 28 of the precipitator may be painted with silverconducting paint as indicated at 29 the paint acting as the secondelectrode. As shown in FIGURE 1 fog enters the precipitator at 30, oilis removed at 31 and gas at 32. The precipitator collects between and50% of the total oil product, depending upon the reactor temperature.For example, at a reactor temperature of 900 F. approximately five timesas much fog oil is produced as is the case at 700 F.

The overhead gas and vapours from the precipitator 26 are passed into asecond water-cooled condenser 33, liquid from this condenser beingpassed to water trap 34 and the oil collected and combined with thecondensed oils from the first condenser and the precipitator as a totaloil product. Wet gases leaving the condenser are preferably partiallyrecycled via line 35 to maintain the desired fiuidization velocity andpressure within the reactor, the gas to be recycled being compressed incompressor 36. Unrecycled gas is passed through charcoal adsorber 37where adsorbable components are removed and the dry gas metered andcollected. An average recovery of 96% of total feed in the laboratorytests may be accounted for on a mass balance basis; the remainder beingaccounted for as gas leaks, char dust, and oil in interconnecting linesand vessels.

The gas mass flow rate through the bed was controlled by a compressorand a bypass valve and measured with a rotameter, the rotameter beingcalibrated for nitrogen at room temperature. Since the fiuidizing gaswas recirculated constantly, it soon became very rich in hydrocarbongases, hydrogen, carbon monoxide and carbon dioxide. This continuousbuildup of gases within the system necessitated a constant removal of aportion of these in order to maintain the desired operation pressure.After one hour of operation, as has been indicated, less than 5% of theoriginal nitrogen remained as part of the recirculating gas. A rotameterreading was chosen so that the bed was operating well within theturbulent fluidized region. This reading was found by plotting thepressure gradients in the bed versus rotameter readings. Good mixing ofthe bed was indicated by equal temperatures at various levels in thebed.

A comparison of the products produced by the carbonibation of Edmontoncoal at 500 C. (932 F.) and fiuidization of Edmonton coal with Leduc oilat 910 F. is shown in Table 1.

TABLE 1 Fluidization (Experiment 1Slurry: 30% coal w./w.):

Total ieed= 18.80 lb.

Feed rate 3.8 lb./hr. Pounds Percent Products:

Product, Feed Percent Oil Analysis:

Sediment 0. 45 2. 40 C residue 1. 45 0. 74 Volatiles 98. 15 96. 86

Total 100. 00 100. 00

Percent Char Analysis:

Ash 11.9 18. 5 Fixed 0 69. 6

Total 100. 0

12,440 B.t.u./lb., dry basis carbonization Percent Products:

Total 100. 0 100. 0

11,940 B.t.u./lb., dry basis Table 1 shows a comparison of a typicalfluidization experiment at 910 F. with a carbonization at a slightlyhigher temperature, for the same coal. While an overall quantitativecomparison is not possible since the systems are not equivalent, e.g. incarbonization there was no contributing oil and the atmosphere was notinert, it is possible to compare the chars formed on a lb./lb. basis.Fluidization gave a char of better heating value and lower ashcontent-both desirable features. Water and other volatiles were removedfrom the coal and petroleum coke was deposited on the char.

Table 2 shows a comparison of the test coals used in the process asdescribed.

*Uncorrected for mineral matter.

Table 3 shows the results of several fluidization runs at varioustemperatures, the analytical results being compared with the oil andcoal feed materials.

TABLE 3 Run 1 2 3 4 5 Oil Feed Bed Temperature, F 875 780 750 TotalFeed, Lb 23. 4 14. 7 17. 9 Feed Rate, Lb./Hr 4. 5 7. 3 3. 6 OilAnalysis:

Gravity, A.P.I 33.0 35. 2 34. 0 Viscosity, cst.:

9. 26 6.32 7. 37 4. 46 4. 17 4. 65 Unsaturates, U, percent 17. 6 15. 811. 8 Asphaltenes, percent 0. 46 0. 20 O. 22 Carbon Residue, percent.Sulfur, percent 0. 28 G. 18 O. 24 Sediment, mg./ml 1. 26 4. 11 3. 70

Ash, percent 12. 7 11.0 10.1 10. 7 Benzene Extractibles, percent. 0. 160. 33 0. 9S 1. 35 Volatiles (dry), percent 18.4 25. 9 26. 1 HeatingValue, B.t.u./Lb.

(Dry Basis) 12, 660 12, 400 12, 170 11, 960 (Dry Ash Free Basis) 14, 50013,920 13, 550 13,400 Gas Produced, S c f lLb. Feed Total 2. 04 0. 25Hz.... 1. 20 O. 02 O0 0. 06 0. 06 CO2" CH4 0. 20 O. 03 Otherhydrocarbons"--. 0. 58 0. 14

In each instance the oil product compares favorably with the feed andthe coal product is markedly improved. It should be obvious that theprocess herein described is something more than a simple resolution of atwo component mixture. It is even more than a simple distillation of thevolatile compounds of each component. Chemical changes are taking place,to the benefit of one or both of the slurry components, as indicated bythe nature of the gas production, and by the character of the oil. Someor all of these beneficial aspects of the process. may be attributed tothe catalytic nature of the surface of the coal char particles at thereaction temperatures involved.

It will be realised that in commercial operation that processingequipment would be modified following the reactor and initialcondensation in FIGURE 1. A practical modification is shown in FIGURE 3wherein the overhead fractions from the existing column would go to acondenser and there would be three liquid fractions produced; one outbeing taken from the middle of the enriching column, though incommercial practice several fractions might be taken off this column andthen go to further processing. As indicated part of the gas stream isrecycled for fluidization.

In other words FIGURE 3 shows how vapors produced in a commercialapplication of the invention might be handled. In this instance thesolids-free vapors are introduced into the side of an enriching orfractionating column comprising a vertical chamber with a number ofperforated horizontal baifle plates. Cooling of the vapors takes placeand substantial portions of the vapors are condensed to liquids whichtend to collect on'the plates, the higher plates collecting the lightoils, i.e. the lowerboiling components, while the lower collect theheavy, i.e. higher-boiling, components. The temperature balance in thecolumn is controlled by the volume of light components recirculated inthe reflux cycle. The enriching fractionating column can be designed toproduce a few oily product streams as illustrated in FIGURE 3 or as manymore as desired. The uncondensed vapors from the column are led to acondenser where cooling Water or air is used to abstract further heatfrom the vapors and a light oil product is recovered. The uncondensedvapors are thus separated from the oily constituents and are availableas product and/or recycle gas stream for the fluidized reactor.

It will be clear however that while this process may have a differentexpression in terms of physical process equipment in commercialpractice, the principles of the process will remain unchanged. Forexample, the heat required for the process may be obtained from (a)cooling of the coal char product, (b) condensation of the overheadvapors, (c) combustion of the process gas, and (d) combustion of coalchar product. Combustion of the process gas as apart of this inventionmay take place in a preheater furnace through which the coal-oil slurryis passed prior to introduction to the fluidized reactor. It may alsotake place in a preheater furnace with the flue gases being used forpart of or all the fluidizing gas stream; alternatively, combustion ofthe fuel gases may take place in the reaction chamber itself through thecontrolled addition of air or oxygen to the system. Heat may be added tothe system by combustion of a part of the char product in substantiallythe same manner as with the process gas. Further, combustion of charparticles to provide process heat may be carried out in a secondfluidized reactor containing char particles,by the addition of oxygen tothe fluidizing stream. The combustion so sustained raises thetemperature of the particles in the reactor, which particles, arerecycled to the distillation reactor to maintain the desired temperaturein that unit.

Since the process in the distillation reactor involves catalysis by thechar particles, another element of this invention is the recognition ofthis priciple and the extension of it through the inclusion of catalystbodies in the reactor chamber to accentuate and direct the desirableeffects arising from such catalysis. Thus, the catalytic aspects of theprocess can be extended and modified through the inclusion of foreigncatalyst bodies directly in the fluidized reactor bed of char particles.A typical catalyst body would be free-flowing screen cylinders or fixedwire grids coated with appropriate substances to produce desired eifectssuch as olefin saturation, aromatics production, hydrocarbon alkylationand general hydrogenation.

We claim: 1. The process of treating coal comprising delivering a"slurry of finely divided coal in crude oil into contact with a bed offluidized coal char particles in a heated reactor maintained at atemperature of about 600 F. to about 1000 F., permitting interactionbetween the oil and the coal, flash-vaporizing the volatiles in the oiland coal and conducting them out of the reactor as a vaporous stream,trapping coal-char particles within the reactor and withdrawing themtherefrom, separating oily and gaseous components from the vaporousstream by condensation and separately recovering the coal solids, oiland gas products.

2. The process of recovering upgraded oil and char products from aslurry of coal and oil comprising slurrying finely-divided coal in crudeoil, introducing the slurry into a fluidized bed of coal char productswithin a reactor maintained at a temperature of about 600 F. to about1000" F., flash-vaporizing the slurry and separating it into twoprincipal phases, a hot oil vaporous phase and an oil-free coal-charparticle phase, maintaining bedpressure and bed-density at apredetermined level by drawing off char from the fluidized bed, passingthe vaporous phase upwardly through a cyclone to separate entrainedsolid particles therefrom, fractionating and condensing the solids-freevaporous phase to form a plurality of oily phases in an enriching columnand condenser, and separating an overhead gas product vapor phase.

3. The process of reacting the components of 'an oilcoal slurry at hightemperature and recovering therefrom an upgraded coal-char product ofenhanced fuel value, in addition to upgraded oil and gas products,comprising introducing a slurry containing 60-80% crude oil and 4020%finely divided coal by Weight into a fluidized bed zone of coal-charparticles within a heated reactor, the temperature of the bed beingabout 850950 F., the bed being fluidized by means of a gas streamcomprising at least one of the group: recycled gas from the reactor andinert gas, the fiuidizing gas being introduced at the bottom of thereactor, heating the slurry within the reactor in order to react the oiland coal components to form a particulate char phase and a vaporoushydrocarbon phase, elements of each phase emanating from both the coaland the oil, predeterm-inining the optimum density of the bed inrelation to the pressure in the reactor and maintaining the desiredreactor temperature and beddensity by withdrawing solids from theparticulate char phase within the bed, removing entrained solids fromthe vaporous hydrocarbon phase, subjecting the vaporous phase to afractionating and condensing step to separate it into a plurality ofoily phases, recovering the oily phases as oils, and recovering gas fromthe vapor phase.

4. The process according to claim 3, the crude oil includingadditionally a composition selected from the group consisting of anadmixture of heavy crude oil and asphalts and an admixture of petroleumresiduum-s and asphalts, the slurry containing about crude oil and about30% finely-divided coal by weight, and the temperature of the bed beingabout 900 F.

5. The process as claimed in claim 3, the fluidized bed containing addedcatalyst substances.

6. The process as claimed in claim 3, the fluidized bed being heated bycombustion of process gas and/or coal char product.

7. The process as claimed in claim 3, the gas product phase beingtreated as an oil-fog in a precipitator thereby forming an additionaloily phase.

8. The process of claim 3 in which the recovered gas is recycled.

References Cited UNITED STATES PATENTS DELBERT E. GANTZ, PrimaryExaminer V, OKEEFE, Assistant Examiner US. Cl. X.R.

